I have a question regarding building a trapped inverted V antenna, for 15/40/80 meter.

Now I have the traps, but they are not resonant in any of the bands, they are resonant on 29.6 MHz (trap1), 14.1 MHz (trap2), 5.5 MHz (trap3)I understand that traps are "lossy" and that they are "most lossy" at resonance frequency.

I was thinking of a configuration, something like this (detailing only 1 leg):

To solve the problem - or even to determine if there is a solution, you need to knowthe L and C values of each trap, not just the resonant frequency. From that you can calculate the effective reactance on each band.

Then you would model an antenna with different wire lengths and these reactancesat each junction to find a combination that works. When using traps that are notresonant at the operating frequency, ALL the wire lengths affect EACH band, so adjustment is not trivial.

Usually you would use a trap with a resonant frequency between the twobands of interest, so you would use traps 2 and 3, but none of the wire lengthsare going to be what you might expect.

Generally speaking, an antenna with two traps and 3 wire sections on each sidewill be resonant on 3 frequencies, but the problem is getting those to fall in thedesired bands with fixed-value traps. The closer the traps are to resonance,the less the impact that the antenna beyond the trap has on the tuning.

And traps really aren't that lossy: there is some advantage in moving the resonantfrequency a bit below the band, but losses are relatively low for a well-built trap,and the simplicity of design and tuning will often argue for using them at or nearresonance. Also, for an inverted vee you want to keep maximum current closer tothe middle of the antenna where the effective height is greater, rather than in theend sections that are closer to the ground, and that requires that the traps becloser to resonance. Otherwise you end up with something more like a 3/2 wavedipole with significant current in the outer sections.

That certainly is the easiest solution. You can build your own traps forother bands as desired.

You can also measure the traps in various ways and calculate the L and C values from that. For example, if you measure the resonant frequencyof the trap with a dip meter, then add 100pf and take another measurement,you can calculate the values close enough to get started.

I would generally recommend starting by choosing what bands you wantthe antenna to cover, then figuring out how to use the parts availableto do that. For example, you could add an external capacitor across the10m trap to move it down to 15m, or you could use the 60m trap to cover 40m and 80m. So with a bit of creativity you may be able to cover15, 20, 40 and 80m using the existing traps.

Of course, if the learning from experimenting is more important than actuallyoperating with the antenna (a familiar situation!) then you can try all sortsof things. In that case I'd suggest starting with dual-band antennas to startwith, as there are fewer variables involved and it is easier to get a usableresult with cut-and-try methods.

You can also measure the traps in various ways and calculate the L and C values from that. For example, if you measure the resonant frequencyof the trap with a dip meter, then add 100pf and take another measurement,you can calculate the values close enough to get started.

Thanks, but I am sure it will take some practice measuring; then again; never to old to learn!

I would generally recommend starting by choosing what bands you wantthe antenna to cover, then figuring out how to use the parts availableto do that. For example, you could add an external capacitor across the10m trap to move it down to 15m, or you could use the 60m trap to cover 40m and 80m. So with a bit of creativity you may be able to cover15, 20, 40 and 80m using the existing traps.

Of course, if the learning from experimenting is more important than actuallyoperating with the antenna (a familiar situation!) then you can try all sortsof things. In that case I'd suggest starting with dual-band antennas to startwith, as there are fewer variables involved and it is easier to get a usableresult with cut-and-try methods.

In that case, the inner wire would be very close to a quarter wave for 20m,and the outer wire will shorter (so the total length is less than a half waveon 40m, due to the loading effect of the trap.) That's probably the easiestantenna, since the 20m tuning is relatively independent of the 40m wirelength. Tune the 20m wire first, then the 40m wire.

Then you can put it up and see if you can notice any difference betweenthat and monoband dipoles for 20m or 40m, as a test of how lossy thetraps really are.

In that case, the inner wire would be very close to a quarter wave for 20m,and the outer wire will shorter (so the total length is less than a half waveon 40m, due to the loading effect of the trap.) That's probably the easiestantenna, since the 20m tuning is relatively independent of the 40m wirelength. Tune the 20m wire first, then the 40m wire.

Then you can put it up and see if you can notice any difference betweenthat and monoband dipoles for 20m or 40m, as a test of how lossy thetraps really are.

I built a 20-40-80 trap dipole with Unadilla traps and expertise from antenna gurus on this forum. I kind of shied away from building my own traps because it was not an exact science and the quality would not be nearly as good. I did end up having to trim the wires to get change the center frequency on the 40 and 80. I have across the board under 2 SWR for the entire 20. I have not experience that losses that people talk about, but even if there is, I do not think they are significant. I am very happy with that antenna.

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